In an optical system that is composed of a plurality of lenses and provided, for example, in a projector or a camera, the refractive index of the lenses may change or a lens barrel that holds the lenses may expand and contract due to changes in the surrounding ambient temperature. This changes the focus position of the optical system, degrading its optical performance.
Patent Literatures 1 and 2 are examples of references that disclose a lens holding device and a lens unit that correct the focus position using a temperature correction member that deforms with temperature changes to inhibit such degradation of optical performance.
The lens holding device disclosed in Patent Literature 1 uses bimetals as the temperature correction member and is configured to directly support the lenses with the bimetals. Due to deformation of the bimetals with temperature changes, the lenses are moved in a direction of an optical axis to thereby correct the focus position.
The lens unit disclosed in Patent Literature 2 is configured to move a holding frame, which holds a correction lens for correcting the focus position, in the direction of the optical axis by the temperature correction member. Various materials such as resins or alloys may be used for the temperature correction member. Among such materials, bimetals deform greatly relative to temperature changes and are thus capable of achieving a large amount of movement in a small space compared to when other materials are used.